1. Field of the Invention
The present invention relates to an intake device for an internal combustion engine for supplying intake air into a combustion chamber of the internal combustion engine. In particular, the present invention relates to an intake device of an internal combustion engine having a rotary tumble control valve generating a tumble flow in a combustion chamber of the internal combustion engine.
2. Description of Related Art
As shown in FIGS. 12A to 12E, there is conventionally a known intake device for an internal combustion engine having a rotary tumble control valve (or rotary throttle valve) generating a tumble flow in a combustion chamber of the internal combustion engine (for example, refer to Patent document 1: JP-A-2005-054603 or Patent document 2: JP-A-2005-105968). The rotary tumble control valve (or the rotary throttle valve) has a rotary valve 101 (a valve member) rotating around its rotational axis line, a duct 102 for rotatably accommodating the rotary valve 101 and an actuator installed to an outside of the duct 102 for driving a rotary shaft of the rotary valve 101.
The rotary valve 101 has a first valve main body 103 located upstream of the rotational axis line of the rotary valve 101 with respect to a flow direction of intake air (i.e., an intake flow direction) and a second valve main body 104 located downstream of the rotational axis line of the rotary valve 101 with respect to the intake flow direction. A link-up passage 105 (a hollow portion) for providing communication between a first intake passage 111 and a second intake passage 112 is provided between the first and second valve main bodies 103, 104.
When a fully-closed opening degree state where the rotary valve 101 is fully closed is defined as a fully closed position (refer to FIG. 12A) and a fully-open opening degree state where the rotary valve 101 is fully open is defined as a fully open position (refer to FIG. 12E), the first and second valve main bodies 103, 104 are structured such that the rotary valve 101 is held at a state of a small opening degree (refer to FIG. 12C) where the rotary valve 101 is slightly opened in a valve-opening operation direction from the fully closed position, i.e., where the rotary valve 101 is half open, during an idling operation of the internal combustion engine.
During the idling operation of the internal combustion engine, a first throttle portion 121 is formed between a cylindrical portion of the duct 102 and a lower end portion (in the figure) of the first valve main body 103 and a second throttle portion 122 is formed between the cylindrical portion of the duct 102 and an upper end portion (in the figure) of the second valve main body 104. The first and second throttle portions 121, 122 constitute portions for throttling passage areas of the first intake passage 111 and the second intake passage 112. The first and second throttle portions 121, 122 have equal opening areas in a low rotation speed region or a low load region of the internal combustion engine. In some cases, the opening area of the second throttle portion 122 is set smaller than the opening area of the first throttle portion 121.
However, in the intake device for the internal combustion engine described in Patent document 1 or 2, when the opening degree of the first throttle portion 121 is set at the small opening degree in order to achieve an intake air quantity necessary for performing the idling operation of the internal combustion engine requiring the tumble flow in the combustion chamber of the internal combustion engine, the opening area of the second throttle portion 122 becomes small since the first valve main body 103 and the second valve main body 104 are mechanically connected with each other. Accordingly, the small opening area of the second throttle portion 122 during the idling operation of the internal combustion engine makes it difficult to generate a strong tumble flow in the combustion chamber of the internal combustion engine.
That is, the intake flow becomes thin rapidly or the passage areas of the first and second intake passages 111, 112 become small rapidly due to the small opening area of the second throttle portion 122, thus causing a thin intake flow along a ceiling wall surface of an intake port of the internal combustion engine. In consequence, the intake flow is strongly influenced by a shape of the intake port of the internal combustion engine, making it difficult to generate an intended tumble flow according to a demand for improving a combustion efficiency in the combustion chamber of the internal combustion engine to improve fuel consumption or the like.